Research Highlights

Southern flounder

Populations
of southern flounder (Paralichthys lethostigma) in Texas have declined
dramatically over recent decades, pointing to the need to understand habitat
requirements at critical early life history stages. This project will examine
low-salinity habitat use and movements of post-settlement juveniles using a
combination of stable isotope and elemental otolith signatures. This work
focuses on southern flounder populations in the Nueces and Aransas-Copano bay
systems in Texas.

Sectioned otolith

Juvenile flounder

Water sampling

This project is being carried out by Megan Nims as part of her Masters
thesis research and is funded by Texas Sea Grant.

Barramundi

Variation in
within-river habitat use and migration patterns is an important yet poorly
understood component of diadromous life history patterns. This project focuses
on the catadromous barramundi (Lates calcarifer) in the Victoria River,
Northern Territory, Australia. This river is nearly 800 km long and unregulated,
allowing a unique opportunity to assess habitat use and spawning frequency in a
minimally-impacted system. We have used a combination of elemental and
isotope ratios to track movement between fresh and marine habitats as well as
specific regions within the river to comprehensively characterize habitat
requirements.

Geochemical records in biogenic carbonate skeletons in hermatypic
corals have long been used to reconstruct variation in environmental parameters
such as temperature, salinity and nutrient availability. This project is
investigating temporal variability in proxies such as Ba/Ca in otoliths of a
site-attached damselfish species (Acanthochromis polyacanthus) and
Porites coral skeletons from inshore and offshore locations on the
Great Barrier Reef. Coupled with long-term water sample analyses, these records
will allow us to investigate temporal variation in freshwater flood pulses and
upwelling events in coral reef habitats.

Population mixing in the marine environment is notoriously difficult to
quantify, and otolith natural tags have allowed unprecedented insight into
stock-specific distributions. Anadromous fish species are ideal candidates for
these investigations because freshwater chemical signatures tend to be
geographically distinct at finer spatial scales than those in the marine
environment. This ongoing work draws upon a large database of ground-truthed
natal signatures from 20 natal rivers across the native range of American shad
(Alosa sapidissima). These signatures are now being used to identify
origins of immature migrants captured in marine environments and compare those
with previous mark-recapture results from adult migrants.